Sheet feeding apparatus and image forming system

ABSTRACT

A sheet feeding apparatus includes a sheet supporting portion, a sheet feeding portion configured to feed a sheet supported on the sheet supporting portion in a sheet feeding direction, an air blow unit including an air blower, an opening portion, a duct configured to form a flow path through which air flows, an adjustment portion configured to vary an opening dimension, the air blow unit being configured to separate a plurality of sheets, including an uppermost sheet, a drive source configured to drive the adjustment portion, and a control unit configured to execute a first mode in which the drive source is controlled such that the opening dimension is set to a first dimension, and a second mode in which the drive source is controlled such that the opening dimension is set to a second dimension that is smaller than the first dimension.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a sheet feeding apparatus configured to feed sheets and an image forming system equipped with the same.

Description of the Related Art

There are many varieties of recording media that can be used to form images in an image forming apparatus such as a copying machine or a printer. Examples of such recording media including OHT (Overhead Transparency) sheets, tracing paper, art paper and coated paper are coated paper, which are characterized in having a smooth surface through which gas is not easily passed. If a plurality of such sheets having a smooth surface through which gas is not easily passed are stored in a sheet feeding unit under a high humidity environment, the sheets tend to be attached to each other, and multi feed in which the sheets are conveyed in an overlapped state may occur. A technique is proposed where air is blown from an air blow unit to the sheets stored in the sheet feeding unit, thereby solving the problem of attaching of sheets (refer to Japanese Patent Application Laid-Open Publication No. 2014-16386).

However, in a state where hot air is blown to separate the sheets as in the air blow unit disclosed in Japanese Patent Application Laid-Open Publication No. 2014-16386, the moisture content of sheet may be reduced excessively if the blowing time of warm air to the sheets to be fed is too long. Especially if the sheets stored in the sheet feeding unit are long-sized sheets, the blowing time of warm air tends to be extended. Excessive reduction of moisture content of the sheet leads to deterioration of image quality, such as blanking of toner image, and causes creases to be formed on the sheet while fixing the toner image on the sheet at the fixing unit, which may cause deterioration of quality of the product.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a sheet feeding apparatus includes a sheet supporting portion configured to support a plurality of sheets, a sheet feeding portion configured to feed a sheet supported on the sheet supporting portion in a sheet feeding direction, an air blow unit including an air blower configured to blow air, an opening portion through which air blown from the air blower is blown out, a duct configured to form a flow path through which air flows between the air blower and the opening portion, an adjustment portion arranged to oppose to an upper surface of the duct and the opening portion and configured to vary an opening dimension in a height direction between the upper surface and the adjustment portion, the air blow unit being configured to separate a plurality of sheets, including an uppermost sheet, among the sheets supported on the sheet supporting portion by air blowing out from the opening portion, a drive source configured to drive the adjustment portion, and a control unit configured to execute, in a state where a length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a first length, a first mode in which the drive source is controlled such that the opening dimension is set to a first dimension, and to execute, in a state where the length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a second length that is longer than the first length, a second mode in which the drive source is controlled such that the opening dimension is set to a second dimension that is smaller than the first dimension.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram illustrating a configuration of an image forming system according to a first embodiment.

FIG. 2 is a cross-sectional view illustrating an internal configuration of a sheet feed deck.

FIG. 3 is a perspective view illustrating the sheet feed deck.

FIG. 4 is a plan view illustrating the sheet feed deck in a state where a storage cabinet is opened.

FIG. 5A is a front view illustrating an opening portion.

FIG. 5B is a side view illustrating the opening portion.

FIG. 6 is a block diagram illustrating a control unit.

FIG. 7 is a graph illustrating a relationship between position of sheet in the sheet feeding direction and moisture content of sheet.

FIG. 8 is a graph illustrating a relationship between warm air blowing time and moisture content Wp of sheet indicated per heater temperature.

FIG. 9 is a graph illustrating a relationship between warm air blowing time and moisture content Wp of sheet indicated per wind speed.

FIG. 10A is an explanatory view illustrating an operation of a shutter in a state where a normal-sized sheet is fed.

FIG. 10B is an explanatory view illustrating an operation of a shutter in a state where a long sheet is fed.

FIG. 11A is a graph illustrating a relationship between number of sheets being fed and moisture content Wp of sheet.

FIG. 11B is a graph illustrating a relationship between elapsed time from start of sheet feed and moisture content Wp of sheet.

FIG. 12 is a flowchart illustrating a sheet feed control.

FIG. 13 is a flowchart illustrating respective steps of an initial separation processing according to a first embodiment.

FIG. 14 is an explanatory view illustrating one example of a setting screen displayed on a display operation unit.

FIG. 15 is an explanatory view illustrating one example of a setting table of heater temperature.

FIG. 16 is an explanatory view illustrating one example of a setting table of fan output.

FIG. 17 is an explanatory view illustrating one example of a setting screen displayed on the display operation unit.

FIG. 18 is a flowchart illustrating respective steps of an initial separation processing according to a second embodiment.

DESCRIPTION OF THE EMBODIMENTS First Embodiment Overall Configuration

A first embodiment according to a present invention will be described. In the following description, up, down, right, left, front and rear directions are illustrated based on a state in which a printer 100 serving as an image forming apparatus is viewed approximately from a front side, in other words, viewpoint of FIG. 1. An image forming system 800 according to a first embodiment includes, as illustrated in FIG. 1, the printer 100, and a sheet feed deck 250 configured to feed sheets to the printer 100. The sheet feed deck 250 is an external apparatus of the printer 100, and it is configured connectably to the printer 100. In a state where the sheet feed deck 250 serving as a sheet feeding apparatus is connected to the printer 100, the sheet P stored in the sheet feed deck 250 can be fed into the printer 100.

The printer 100 is a laser beam printer adopting an electrophotographic system. The printer 100 includes, as illustrated in FIG. 1, a sheet feeding unit 240 configured to feed the sheet P being supported, an image forming unit 120 configured to form an image on the sheet P being fed, and a control unit 700 configured to control an image forming operation. Further, the printer 100 includes a fixing unit 170 configured to fix a transferred image on the sheet P, and sheet discharge roller pairs 13 and 12 configured to discharge the sheet P on which an image has been fixed to sheet discharge trays 27 and 200. The sheet discharge tray 27 is arranged on an upper portion of an apparatus body 110, and a sheet discharge tray 200 is arranged on a left side of the apparatus body 110.

An image forming unit 120 constitutes a so-called four-drum full color image forming unit including a laser scanner 122, four process cartridges 123 and an intermediate transfer portion 130. The process cartridges 123 form toner images of respective colors, which are yellow (Y), magenta (M), cyan (C) and black (K). The respective process cartridges 123 include a photosensitive drum 5, a developing unit 6, a charging unit 7, a cleaner 8 and so on. Toner cartridges 121 respectively storing color toner of each color are detachably attached to the apparatus body 110 at an area above the image forming unit 120.

The intermediate transfer portion 130 includes an intermediate transfer belt 9 d serving as an intermediate transfer body, primary transfer rollers 10Y, 10M, 10C and 10K, a drive roller 9 a, a tension roller 9 b, and a secondary transfer inner roller 9 c. The intermediate transfer belt 9 d is wound around and supported by rollers including the drive roller 9 a, the tension roller 9 b and the secondary transfer inner roller 9 c, and in a state where the drive roller 9 a is driven to rotate, the intermediate transfer belt 9 d is rotated in a direction of arrow D1 illustrated in FIG. 1. Further, the intermediate transfer belt 9 d is arranged below the four process cartridges 123 and in contact with the photosensitive drums 5 of the respective process cartridges 123.

The primary transfer rollers 10Y, 10M, 10C and 10K are arranged to contact an inner circumferential surface of the intermediate transfer belt 9 d at positions opposed to the photosensitive drums 5 of the respective colors. Primary transfer portions are formed between respective photosensitive drums 5 and the intermediate transfer belt 9 d. Further, a secondary transfer outer roller 11 is arranged at a position opposed to the secondary transfer inner roller 9 c with the intermediate transfer belt 9 d interposed therebetween. The secondary transfer outer roller 11 is in contact with an outer circumferential surface of the intermediate transfer belt 9 d. The intermediate transfer belt 9 d and the secondary transfer outer roller 11 constitute a secondary transfer portion.

A sheet feeding unit 240 includes cassettes 150 and 220 on which sheets P are supported, and a manual feed tray 210. The cassettes 150 and 220 are arranged at a lower portion of the apparatus body 110, for example, and are configured to be inserted to the apparatus body 110 in a detachable manner. The manual feed tray 210 is arranged at a right side of the apparatus body 110.

In a state where the printer 100 receives a command to start image forming operation, the photosensitive drum 5 rotates, and a surface of the photosensitive drum 5 is charged uniformly by the charging unit 7. Then, the laser scanner 122 modulates and outputs a laser beam based on an image data entered from an input interface or an external computer. The laser scanner 122 outputs laser beams and scans the surface of the respective photosensitive drums 5, thereby forming electrostatic latent images based on image data on the surface of the respective photosensitive drums 5. That is, electrostatic latent images of yellow (Y), magenta (M), cyan (C) and black (K) are sequentially formed on the photosensitive drums 5 of the respective process cartridges 123. The formed electrostatic latent images of yellow, magenta, cyan and black are visualized by toner supplied from the developing unit 6, and form yellow, magenta, cyan and black toner images. By having transfer voltage applied to the primary transfer rollers 10Y, 10M, 10C and 10K, the yellow, magenta, cyan and black toner images formed on the respective photosensitive drums 5 are sequentially transferred in a superposed manner to the intermediate transfer belt 9 d. Thereby, a full-color toner image is formed on the intermediate transfer belt 9 d. The toner remaining on the respective photosensitive drums 5 after the toner images are transferred is collected by the cleaner 8.

Meanwhile in the printer 100, in parallel with the image forming operation, the sheet P is picked up by the sheet feeding unit 240 from a selected storage location of the sheet P and is fed to the image forming unit 120. In the case of the printer 100 illustrated in FIG. 1, one storage location of the sheet P is selected from the cassette 150, the cassette 220, the manual feed tray 210 and the sheet feed deck 250. Here, we will describe a case where the cassette 150 was selected as an example of the storage location of the sheet P.

If the cassette 150 is selected as the storage location of the sheet P, the sheets P stored in the cassette 150 are sent by a pickup roller 151 and are separated one by one by a feed roller 22 and a separation roller 21. The sheet P separated one by one is conveyed by conveyance roller pairs 153, 154 and 155 arranged on a conveyance path 20 to a registration roller pair 161. A leading edge of the sheet P being conveyed to the registration roller pair 161 is abutted against a nip of the registration roller pair 161, by which skewing of the sheet is corrected. Thereafter, the sheet P is conveyed to the secondary transfer portion at a matched timing with the toner image borne on the intermediate transfer belt 9 d. The toner image borne on the intermediate transfer belt 9 d is transferred collectively to the sheet P by a secondary transfer bias applied to the secondary transfer outer roller 11. The sheet P to which the toner image has been transferred is conveyed to a fixing unit 170, and the sheet P is subjected to heat and pressure by a fixing roller 171 and a pressure roller 172. Thereby, the toner image on the sheet P is fixed to the sheet P.

In a state where image formation to the sheet P has been completed, the sheet P on which the toner image has been fixed is conveyed to a conveyance path 231, the conveyance destination being switched by the switching member 173. If the sheet discharge tray 200 is selected as a discharge destination, the sheet P conveyed to the conveyance path 231 is guided through the conveyance path 231 to a sheet discharge path 180 by a switching member 174 arranged on the conveyance path 231. The sheet P guided to the sheet discharge path 180 is discharged by a sheet discharge roller pair 12 arranged on the sheet discharge path 180 to the sheet discharge tray 200. Further, if the sheet discharge tray 27 is selected as a sheet discharge destination, the sheet P conveyed to the conveyance path 231 is guided by the switching member 174 through the conveyance path 231 to a sheet discharge path 181. The sheet P having been guided to the sheet discharge path 181 is discharged by a sheet discharge roller pair 13 arranged on the sheet discharge path 181 to the sheet discharge tray 27.

Meanwhile, in a state where images are formed on both sides of the sheet P, the sheet P on which an image has been formed on a first side is guided by the switching member 173 to a reverse conveyance path 17. The sheet P guided to the reverse conveyance path 17 is temporarily conveyed to a reverse conveyance path 16 by conveyance roller pairs 14 and 15. After the sheet P has been conveyed to the reverse conveyance path 16, the conveyance roller pair 15 is reversed, and the sheet P is conveyed to a duplex conveyance path 18 by the conveyance roller pair 15 rotated in reverse rotation and a switching member 175. The sheet P having been conveyed to the duplex conveyance path 18 is further conveyed from the duplex conveyance path 18 to the conveyance path 20 by a conveyance roller pair 19, and thereafter conveyed to the registration roller pair 161. Then, similar to forming an image to the first side described earlier, image is formed on a second side of the sheet P.

Sheet Feed Deck

Next, the sheet feed deck 250 will be described in detail. As illustrated in FIGS. 1 through 3, the sheet feed deck 250 includes a lifter 507 serving as a sheet supporting portion configured to support a plurality of sheets P, a storage cabinet 506 configured to store the lifter 507, and a lifting mechanism 530 configured to lift the lifter 507. The storage cabinet 506 is configured to be opened and closed with respect to a deck body when a storage cabinet open/close button 510 is pressed.

The storage cabinet 506 is capable of storing a long sheet whose length in a sheet feeding direction denoted by arrow D2 (refer to FIG. 2) (hereinafter simply referred to as “sheet length”) is longer than a sheet used in general. In the present embodiment, a long sheet refers to a sheet having a sheet length that exceeds 19 in. (approximately 482.6 mm). Further, a sheet having a sheet length shorter than 19 in., that is, a sheet having a sheet length that is shorter than the long sheet, is referred to as a normal-sized sheet.

Further, the sheet feed deck 250 includes a pickup roller 501 configured to feed an uppermost sheet supported on the lifter 507, and a feed roller 502 and a separation roller 503 configured to separate the fed sheets P one by one and conveying the same. The sheet P having been separated one by one by the feed roller 502 and the separation roller 503 is drawn into the printer 100 by draw-in rollers 504 and 505 provided in the printer 100. The pickup roller 501, the feed roller 502, the separation roller 503 and the draw-in rollers 504 and 505 are formed so that the outer circumferential surfaces thereof that come in contact with the sheet P are formed of a material having a high friction coefficient, such as rubber.

The lifting mechanism 530 includes, as illustrated in FIG. 2, two driven pulleys 530 b, and a lifter motor 500 that winds up and down a wire 530 a wound around the two driven pulleys 530 b. The wire 530 a has a first end connected to the lifter 507 and a second end connected to the lifter motor 500. The lifter 507 is lifted by having the lifter motor 500 wind up the wire 530 a and is lowered by having the lifter motor 500 wind down the wire 530 a. The ends of the wire 530 a are respectively connected to both ends of the lifter 507 in the width direction, so that it can lift the lifter 507 stably.

Further, a sheet presence detection sensor 601, a sheet height detection sensor 602, a sheet feed sensor 603, a bottom position detection sensor 604 and a replenishment position detection sensor 605 are arranged in the sheet feed deck 250. Further, a storage cabinet open/close detection sensor 608 for detecting the opening/closing of the storage cabinet 506 and an environment sensor 614 (refer to FIG. 6) that is not shown in FIG. 2 are arranged in the storage cabinet 506.

Now, the sheet presence detection sensor 601 is a sensor that detects the presence of the sheet P supported on the lifter 507, and for example, it is arranged close to the pickup roller 501 serving as a sheet feeding portion. The sheet height detection sensor 602 is a sensor that detects whether an uppermost surface of the sheet P supported on the lifter 507 is positioned at a feed position in which the sheet can be fed by the pickup roller 501, and for example, it is arranged near the pickup roller 501. The sheet feed sensor 603 is a sensor that detects that the sheet P supported on the lifter 507, that is, the sheet P stored in the sheet feed deck 250, has passed a predetermined position, such as an exit through which the sheet P is fed from the sheet feed deck 250 (hereinafter referred to as “sheet feed port”). The sheet feed sensor 603 is arranged near the sheet feed port, for example, and it enables to detect that the leading edge and the trailing edge of the sheet P in the sheet feeding direction has passed the sheet feed port.

The bottom position detection sensor 604 and the replenishment position detection sensor 605 detect the position of the lifter 507 in a stacking direction. The bottom position detection sensor 604 is a sensor arranged at a lower portion of the storage cabinet 506 to detect that the lifter 507 is at a lowermost position in the storage cabinet 506. The replenishment position detection sensor 605 is a sensor arranged below the separation roller 503 and detects that a remaining amount of sheets P supported on the lifter 507 has been reduced based on the position of the lifter 507 in the stacking direction. The environment sensor 614 is a sensor that detects an environmental condition inside the storage cabinet 506, that is, the environmental condition including a temperature (atmospheric temperature) and humidity of ambient atmosphere of the sheet P supported on the lifter 507.

Further, as illustrated in FIGS. 2 through 4, the sheet feed deck 250 includes a trailing edge regulating plate 2 that regulates a trailing edge position in the sheet feeding direction of the sheet P supported on the lifter 507, and side regulating plates 610 a and 610 b that regulate positions of both edge portions of the sheet in the width direction. The width direction illustrated by arrow D4 in FIG. 3 is a direction orthogonal to the sheet feeding direction illustrated by arrow D2.

Air Blow Unit

An air blow unit 620 for blowing separation air for separating sheets to a plurality of sheets including the uppermost sheet among the sheets from the uppermost sheet to the lowermost sheet stored in a stacked manner in the storage cabinet 506 is arranged on the side regulating plate 610 a, as illustrated in FIG. 4. The air blow unit 620 includes a warm air blowing portion 620 a that discharges air (hereinafter referred to as “warm air”) 24 a that is heated to a temperature higher than the ambient temperature in the storage cabinet 506, and a cool air blowing portion 620 b that discharges the ambient air as a cool air 24 b.

The warm air blowing portion 620 a includes a fan 611 a serving as an air blower, an air heater 613 serving as a heater, a shutter 615 a serving as an adjustment portion and a swing member, and an opening portion 612 a from which warm air 24 a serving as the separation air is blown out. An air intake duct 618 and an exhaust duct 617 a are respectively connected to an air intake side and an exhaust side of the fan 611 a. The air heater 613 is arranged inside the air intake duct 618. The shutter 615 a serving as an adjustment portion is arranged near the opening portion 612 a at an exit portion of the exhaust duct 617 a serving as a duct, and is configured to enable a height of a flow path FP formed within the exhaust duct 617 a to be adjusted within a range of height of the exhaust duct 617 a.

More specifically, the shutter 615 a is arranged to oppose to an upper surface 619 of the exhaust duct 617 a, as illustrated in FIGS. 5A and 5B, and is configured to have an upper end side of the shutter 615 a swing about a swing shaft 616 a arranged at a lower end portion of the exhaust duct 617 a. The swing shaft 616 a is connected to a shutter motor M1 serving as a drive source, and the shutter 615 a is capable of swinging in an air blowout direction by transmission of drive from the shutter motor M1. The shutter 615 a adjusts the height of the flow path FP by changing an opening dimension h from the upper surface 619 of the exhaust duct 617 a in a height direction to adjust the height of the flow path FP. Further, from a viewpoint of enhancing effect of sheet separation, the shutter 615 a is controlled by a control unit 700 described later (refer to FIG. 6) to swing continuously during a sheet feeding job in which the pickup roller 501 feeds the sheet.

The cool air blowing portion 620 b includes, as illustrated in FIG. 4, a fan 611 b serving as an air blower, a shutter 615 b serving as an adjustment portion and a swing member, an exhaust duct 617 b serving as a duct, and an opening portion 612 b through which the cool air 24 b serving as a separation air is blown out. The fan 611 b, the shutter 615 b, the exhaust duct 617 b and the opening portion 612 b are respectively configured similarly as the fan 611 a (refer to FIG. 4), the shutter 615 a (refer to FIG. 5A), the exhaust duct 617 a and the opening portion 612 a.

Further, the opening portion 612 a at the warm air blowing portion 620 a and the opening portion 612 b at the cool air blowing portion 620 b are arranged to correspond to a height of the pickup roller 501 (refer to FIG. 2) in a height direction indicated by arrow D3, as illustrated in FIG. 3. Further, the opening portion 612 a is arranged to overlap with a contact portion where the pickup roller 501 in the sheet feeding position and the uppermost sheet stored in the storage cabinet 506 come into contact when viewed in a width direction indicated by arrow D4.

According to the sheet feed deck 250 configured as above, long sheets can be stored in the storage cabinet 506, and the portion of the trailing edge in the sheet feeding direction of the sheet P stored in the storage cabinet 506 is determined by moving the trailing edge regulating plate 2. Further, both ends of the sheet P in the width direction are positioned by moving the side regulating plates 610 a and 610 b. The exhaust duct 617 a illustrated in FIGS. 5A and 5B illustrate one of the exhaust ducts 617 a and 617 b as an example. That is, the other exhaust duct 617 b of the exhaust ducts 617 a and 617 b is also configured similarly as the exhaust duct 617 a.

Control Unit

The control unit 700 controls the image forming operation in the image forming system 800 (refer to FIG. 1). The control unit 700 includes, as illustrated in FIG. 6, a CPU 301, a memory 302, an I/O port 303 and a communication interface 304. Further, the control unit 700 is connected in a manner capable of telecommunicating respectively with a display operation unit 310 serving as a user interface (hereinafter referred to as “UI”), a host device 600, an image forming unit 120, a fixing unit 170 and a storage cabinet control unit 320.

The storage cabinet control unit 320 is connected in a manner capable of telecommunicating with an interface that receives input of command, a timer, various sensors, and various components composed of devices being the target of control. The above-mentioned interface includes the storage cabinet open/close button 510 that receives input of an open command and a close command of the storage cabinet 506 (refer to FIG. 1) from the user. The above-mentioned timer includes a timer 26 that measures an elapsed time from a designated timing, such as from a start of blowing of separation air to the sheets P. The various sensors include the storage cabinet open/close detection sensor 608, the bottom position detection sensor 604, the replenishment position detection sensor 605, the environment sensor 614, the sheet presence detection sensor 601, the sheet height detection sensor 602, a size detection sensor 4 and the sheet feed sensor 603. The equipment being a control target of the storage cabinet control unit 320 includes a storage cabinet open/close solenoid 23, the lifter motor 500, the air heater 613, the shutter motor M1 and the fans 611 a and 611 b. The storage cabinet open/close solenoid 23 is a solenoid assembled to a latch member (not shown) of the storage cabinet 506, and upon receiving an open command and a close command of the storage cabinet 506 by the storage cabinet open/close button 510, the lock of the storage cabinet 506 is disengaged or engaged.

Relationship Among Moisture Content of Sheet, Multi Feed and Paper Creases

Next, a relationship among moisture content of the sheet P (hereinafter referred to as “moisture content of sheet”), multi feed of the sheet P and creases on the sheet P (hereinafter referred to as “paper creases”) that occur when the toner image is fixed in the fixing unit 170 (refer to FIG. 1) will be described. In the present description, we focused on three parameters, which are a time during which the warm air 24 a (refer to FIG. 4) is blown onto the sheet P (hereinafter referred to as “warm air blow time”), a set temperature of the air heater 613 (hereinafter referred to as “heater temperature”), and a wind speed of the fan 611 a.

At first, a relationship between the moisture content of sheet and the warm air blowing time will be described. The graph illustrated in FIG. 7 illustrates the relationship between sheet position in the sheet feeding direction and the moisture content of the sheet of cases where types, grammage and size of the sheet P stored in the storage cabinet 506 (refer to FIG. 1), and the heater temperature and blow position are not varied, but with the warm air blowing time of the warm air blown to the sheet P varied in six patterns. Specifically, curves C1 through C6 illustrated in FIG. 7 respective show moisture contents of sheets where the respective warm air blowing time is 10 sec., 50 sec., 100 sec., 180 sec., 240 sec. and 360 sec.

Regarding FIG. 7, the type, grammage and size of the sheet P used to acquire the results shown in FIG. 7 are, respectively, coated paper, 80 [g/m²] and A3 size (297 [mm]×420 [mm]). Sheet feeding direction position [mm] on a horizontal axis defines that a leading edge positioned most upstream in the sheet feeding direction of the sheet P stored in the storage cabinet 506 (refer to FIG. 1) is defined as 0 [mm]. Further, a position where the sheet feeding direction position is x [mm] is a center position in the sheet feeding direction of the opening portion 612 a that blows the warm air 24 a (refer to FIG. 5B) to the sheet P, and in the example illustrated in FIG. 7, x equals 70 [mm]. Further, the moisture content Wp of sheet is the moisture content at the position where the sheet feeding direction position is x [mm] where the moisture content is lowest. Further, the moisture content W of sheet is an average moisture content of the sheet P excluding the portion onto which the warm air 24 a is blown.

As illustrated in FIG. 7, the moisture content Wp of sheet is reduced as the warm air blowing time has been elongated from 10 sec. to 50 sec., 100 sec., 180 sec., 240 sec. and 360 sec. The moisture content W of sheet was scarcely influenced by the change of warm air blowing time.

Next, with reference to FIG. 8, we will describe how the moisture content Wp of sheet has changed with respect to warm air blowing time when the heater temperature was changed. The sheet P used to achieve the results illustrated in FIG. 8 is similar to the sheet P used to achieve the result illustrated in FIG. 7. Curves C7, C8 and C9 illustrated in FIG. 8 respectively illustrate transition of moisture content Wp of sheet with respect to the warm air blowing time in a case where the heater temperature is respectively set to 60 [° C.], 90 [° C.] and 110 [° C.]. In comparing the inclination of deterioration of moisture content in a state where the warm air blowing time of curves C7, C8 and C9 are set to 0 to 50 sec., it can be recognized that as the heater temperature rises, the inclination of deterioration of moisture content increases, and the speed of deterioration of moisture content per unit time is increased. Further, it was recognized that the moisture content Wp of sheet illustrated by curved lines C7, C8 and C9 will change very little after the warm air blowing time becomes longer than 300 seconds. Further, it can be recognized that as the heater temperature rises, the finally converged moisture content becomes low, and the time required to converge to the moisture content is short. Further, in the case where the heater temperature is 90 [° C.] and 110 [° C.], it was recognized that the finally converged moisture content Wp of sheet falls within range R2, that is, as described later, low so that paper creases will be generated during fixing of the toner image.

Next, we will describe a result of experiment performed by the present inventors regarding the relationship among moisture content Wp of sheet, the multi feed and the generation of paper creases on the sheet P. The present experiment was performed in a room with an atmospheric temperature of 30 [° C.] and a humidity of 80 [%], and the type, grammage [g/m²] and size of the sheet P being used are, respectively, the same as the type, the grammage [g/m²] and the size of the sheet P being used to acquire the results of FIG. 7. The moisture content Wp of sheet at the start of experiment of the sheet P is 8.0 [%].

As a result of the experiment, the present inventors have obtained knowledge that the moisture content Wp of the sheet should be reduced to 7.4 [%] or lower to relieve the attachments of sheets and feed the sheets P without causing multi feed. The range of the moisture content Wp of the sheet enabling to prevent multi feed of the sheet P (Wp≤7.4 [%]) is range R1 illustrated in FIG. 8 and FIG. 9 described later. Specifically, in order to feed the sheet P without causing multi feed, based on the relationship with the heater temperature illustrated in FIG. 8, if the heater temperature is set respectively to 60 [° C.], 90 [° C.] and 110 [° C.], warm air blowing time of respectively approximately 40 sec., 15 sec., and 8 sec. are required.

Further, the present inventors have also obtained knowledge that if the moisture content Wp of sheet is reduced to 4.2 [%] or lower, paper creases may be formed on the sheet P during fixing of toner image at the fixing unit 170 (refer to FIG. 1), and the quality of the product was deteriorated. The range of moisture content Wp of sheet in which paper creases were generated to the sheet P (Wp≤4.2 [%]) is range R2 illustrated in FIG. 8 and FIG. 9 described later. Specifically, based on the relationship with the heater temperature illustrated in FIG. 8, if the heater temperature is set to 60 [° C.], even if the warm air blowing time is set to a long time exceeding 300 sec., paper creases will not be generated to the sheet P during fixing of the toner image. Meanwhile, if the heater temperature is set to 90 [° C.] or to 110 [° C.], respectively, paper creases will be generated to the sheet P during fixing of the toner image if the warm air blowing time is approximately 170 sec. or longer or 80 sec. or longer. Based on this result, it can be recognized that if the heater temperature is 60 [° C.], the warm air blowing time should be approximately 40 sec. or longer to not cause multi feed of the sheet P and prevent deterioration of product quality. If the heater temperature is 90 [° C.], the warm air blowing time should be approximately 15 sec. or more and less than 170 sec. to not cause multi feed of the sheet P while preventing deterioration of quality of the product. Further, if the heater temperature is 110 [° C.], the warm air blowing time should be approximately 8 sec. or more and less than 80 sec.

Next, with reference to FIG. 9, we will describe how the moisture content Wp of sheet has changed with respect to the warm air blowing time in a state where the wind speed is varied by changing the rotational speed of the fans 611 a and 611 b (refer to FIG. 4). The curved lines C10, C11 and C12 illustrated in FIG. 9 respectively show the transition of moisture content Wp of sheet with respect to warm air blowing time in a state where the wind speed is set to three speeds, a low speed which it the slowest, a medium speed which is the second slowest, and a high speed which is the fastest. It was recognized that the moisture content Wp of the sheet was finally converged to the same moisture content of the sheet regardless of whether the wind speed is set to low speed, or curve C10, to medium speed, or curve C11, or to high speed, or curve C12. Further, it was recognized that the time required for the moisture content Wp of sheet to converge was shorter as the wind speed increases.

However, as the wind speed increases, the behavior of the sheet P becomes unstable, and the contact between the sheet P and the pickup roller 501 (refer to FIG. 1) becomes unstable, so that conveyance failure of the sheet P tends to occur. Therefore, there is an upper limit set to the wind speed to prevent conveyance failure of the sheet P. The upper limit of the wind speed that does not cause conveyance failure of the sheet P is determined by the type or the grammage of the sheet P. For example, as the grammage of the sheet P reduces, the behavior of the sheet P tends to become unstable by being affected by the wind, so that the wind speed must be lowered.

Relationship Between Sheet Length and Warm Air Blowing Time

In the present description, the following conditions (1) to (3) are presupposed. (1) If a job for feeding k number of sheets P (wherein k is a natural number) is entered, warm air 24 a (refer to FIG. 4) is blown from immediately before feeding of the first sheet P or uppermost sheet from the storage cabinet 506 (refer to FIG. 1) to feeding of the kth sheet or final sheet. (2) A sheet separation ability for separating the sheets P stacked and stored in the storage cabinet 506 is, for example, 20 sheets in a state where the shutter 615 a (refer to FIG. 5A) is opened to a maximum opening state. (3) The speed and interval between sheets while feeding the sheets P is not varied regardless of the difference in sheet length of the sheet P.

At first, we will focus on the stacking direction of the sheet P being fed. If the above presuppositions (1) through (3) are satisfied, if a job to feed sheets P is received, the sheets P positioned from the first to the twentieth sheets among all the sheets from the uppermost sheet to the lowermost sheet stacked and stored in the storage cabinet 506 are separated by the warm air 24 a. Each time a sheet P is fed, the uppermost sheet is fed and each sheet moves up closer to the top. Therefore, if k represents 20 sheets or less, the sheet P receiving the blow of warm air 24 a the longest before being fed is the kth sheet from the uppermost sheet. The sheet P which is the 21st sheet at the time the feeding of sheets P is started will not receive blow of warm air 24 a at the time the feeding of sheets P is started, but it receives blow of warm air 24 a after it has become the 20th sheet, and continues receiving blow until it is fed. Therefore, the warm air blowing time for the 21st sheet to the kth sheet is the same as the warm air blowing time of the sheet P that is positioned as the 20th sheet at the time feeding has been started.

Operation Control of Shutter

Next, operation control of the shutters 615 a and 615 b will be described. Since the shutters 615 a and 615 b are operated similarly, in the following description, the operation control of only the shutter 615 a will be described. The shutter 615 a can be operated according to a first mode illustrated in FIG. 10A and a second mode illustrated in FIG. 10B. In other words, the control unit 700 is capable of executing either a first mode or a second mode, based on which the operations of the shutter 615 a differs. In the first mode, the shutter 615 a swings between a closed position A where the flow path FP defined by the exhaust duct 617 a is most closed and an opened position B where the flow path FP is opened the most, as illustrated in FIG. 10A. In further detail, during the sheet feeding job, the shutter 615 a swings continuously within the range from the closed position A to the opened position B. Thereby, air flowing through the opening portion 612 a is fluctuated and the sheet P can be separated efficiently. The swing angle of the opened position B in a state where the closed position A is set as reference (0 degrees) is angle θ₁.

That is, in a first mode where the normal-sized sheet which is a sheet having a first length is fed, the shutter 615 a swings with angle θ₁ set as a maximum swing angle. Then, in the opened position B, an opening dimension where the shutter 615 a is positioned becomes a first dimension h1. That is, in a state where the control unit 700 executes the first mode, the swing angle θ₁ of the shutter 615 a from the closed position where the opening dimension is set to the first dimension h1 becomes maximum. The closed position is a position where the opening dimension h becomes minimum.

Further, in the second mode, the shutter 615 a swings between the closed position A and an intermediate position C, as illustrated in FIG. 10B. The intermediate position C is a position between the closed position A and the opened position B. In further detail, the shutter 615 a swings continuously within the range between the closed position A and the intermediate position C during the sheet feeding job. Thereby, air sent out from the opening portion 612 a is fluctuated and the sheet P can be separated efficiently. The swing angle of the intermediate position C in a case where the closed position A is set as reference (0 degrees) is angle θ₂.

That is, in the second mode for feeding a long sheet having a second length that is longer than the first length, the shutter 615 a swings with angle θ₂ set as the maximum swing angle. Then, in the intermediate position C, the opening dimension at which the shutter 615 a is positioned is set to a second dimension h2 that is smaller than the first dimension h1 (h2<h1). That is, in a state where the control unit 700 executes the second mode, the swing angle θ₂ from the closed position where the opening dimension is the second dimension h2 becomes the maximum swing angle for the shutter 615 a. As described, by operating the shutter 615 a by a first mode and a second mode, the opening dimension h can be varied, and the height of the air blown toward the sheet P stacked on the lifter 507 can be varied. For example, in the first mode, air can be blown to the top 20 sheets including the uppermost sheet of all the sheets P stacked on the lifter 507. Further, in the second mode, air can be blown to the top 10 sheets including the uppermost sheet of all the sheets P stacked on the lifter 507.

Relationship Between Warm Air Blow Time and Moisture Content of Sheet

FIG. 11A is a graph illustrating a transition of moisture content of the sheet P along with the progression of number of sheets being fed, and FIG. 11B is a graph illustrating a transition of moisture content of the sheet P along with the sheet feed time from the start of feeding of sheets. The moisture content of sheet mentioned here refers to the moisture content Wp of the sheet at the position to which warm air is blown and where the moisture content is most lowered.

Curved lines C13 and C16 in FIGS. 11A and 11B illustrate cases where the shutters 615 a and 615 b are operated in the first mode, and where the sheet length of the sheet P being fed is 30 in., that is, a long sheet. Curved lines C14 and C17 illustrate cases where the shutters 615 a and 615 b are operated in the first mode, and where the sheet length of the sheet P being fed is 19 in., that is, a normal-sized sheet. Curved lines C15 and C18 illustrate cases where the shutters 615 a and 615 b are operated in the second mode, and where the sheet P being fed is the long sheet. In all the sheets being fed shown by curved lines C13 through C18, only the size of the sheet differs, and the type and grammage of the sheet are the same.

By comparing the curved lines C13 and C14 illustrated in FIG. 11A, in view of the advancement of the number of sheets being fed, it can be recognized that the pace in which the moisture content drops is faster in long sheets than in normal-sized sheets. By comparing the curved lines C16 and C17 illustrated in FIG. 11B, it can be recognized that the pace in which the moisture content drops is not so different regardless of the length of the sheet, if the elapsed time from the start of feeding of sheets is the same.

If the above-mentioned presuppositions (1) through (3) are satisfied, the sheet feed time of the first sheet P is varied according to the sheet length, since it is proportional to the sheet length. Further, the warm air blowing time to one sheet P is elongated as the length of sheet feed time of the sheet P is elongated. That is, the warm air blowing time to one sheet P is longer if the sheet P being fed is the long sheet compared to the case where the sheet P being fed is the normal-sized sheet. Further, by referring to the curved lines C13 and C14 of FIG. 11A, the moisture content of a long sheet is dropped to approximately 4% but drop of the moisture content of a normal-sized sheet is converged to approximately 5%. This is considered to have been caused by the fact that when a long sheet is fed, the blow time of the warm air 24 a that one sheet receives from the time the lifter 507 is lifted to the feeding of the 20th sheet from the top sheet of the sheet bundle is long.

Therefore, in a state where the long sheet is fed, excessive drop of moisture content of sheet tends to occur compared to the case where a normal-sized sheet is fed, and product quality deterioration due to the excessive drop of moisture content of sheet tends to occur. Therefore, according to the present embodiment, as described later, sheet feed control is performed, and the operation mode of the shutters 615 a and 615 b is controlled so that the warm air blowing time to the sheet P becomes equivalent in cases where a long sheet is fed and where a normal-sized sheet is fed.

That is, if a normal-sized sheet is fed, the shutters 615 a and 615 b are operated in a first mode. In a state where the shutter 615 a is operated by a first mode, the opening dimension h is relatively large, so that a large number of sheets receive blow of the warm air 24 a, according to which sheets can be separated preferably. Meanwhile, upon feeding long sheets, the shutters 615 a and 615 b are operated in a second mode. In a state where the shutter 615 a is operated in a second mode, the opening dimension h is relatively small, so that the number of sheets to which the warm air 24 a is blown is reduced. Therefore, even if the sheet length is long, the total time during which the warm air 24 a is blown to the sheet being fed can be suppressed, and as shown by the curved lines C15 and C18 of FIGS. 11A and 11B, excessive drop of the moisture content of sheet can be prevented. Further, if the number of sheets to which the warm air 24 a is blown is small, the sheet separation ability is deteriorated, but in the case of a long sheet, the sheet feed time per sheet is long so that there is no problem.

Sheet Feed Control

Next, with reference to the flowcharts of FIGS. 12 and 13, sheet feed control of a state where the sheet P is fed from the sheet feed deck 250 will be described. The flowchart of FIG. 12 illustrates a sheet feed control of a state where the copy job is entered in step S7. As illustrated in FIG. 12, at first, the storage position, type, grammage and size of the sheet being fed are selected by the user operating the display operation unit 310 (step S1). FIG. 14 illustrates an example of a setting screen 25 displayed on the display operation unit 310, wherein the user selects one sheet attribute from a plurality of sheet attributes displayed on the setting screen 25.

Next, the control unit 700 determines whether the storage position of the sheet being fed is the sheet feed deck 250 based on sheet attribute information selected by the user in step S1 (step S2). If the storage position of the sheet being fed is not the sheet feed deck 250 (step S2: NO), the present processing is ended.

If the storage position of the sheet being fed is the sheet feed deck 250 (step S2: YES), the control unit 700 acquires environment information including the atmospheric temperature and humidity in the storage cabinet 506 by the environment sensor 614 arranged in the storage cabinet 506 (step S3). Then, the control unit 700 determines whether initial separation processing of the sheet bundle by warm air 24 is necessary based on the acquired environment information and the sheet attribute information (step S4).

In a state where initial separation processing is determined necessary (step S4: YES), the initial separation processing is performed (step S5). Detailed processing of the initial separation processing will be illustrated in the flowchart of FIG. 13. As illustrated in FIG. 13, the control unit 700 determines the heater temperature of the air heater 613 and the output of the fans 611 a and 611 b based on the acquired environment information and the sheet attribute information (step S501).

FIG. 15 is a setting table of heater temperature, and FIG. 16 is a setting table of fan output. The tables of FIGS. 15 and 16 illustrate heater temperature and fan output of a case where the sheet type of the sheet P is coated paper and the grammage is 80 to 150 [g/m²], but a plurality of tables corresponding to different sheet attribute information can be prepared. The tables are stored in the memory 302.

The setting table of the heater temperature illustrated in FIG. 15 has atmospheric temperature and humidity detected by the environment sensor 614 respectively set to three levels. The atmospheric temperature is set to three levels, which are, from the lower temperature, lower than 20 [C° ], 20 [° C.] or higher and lower than 30 [° C.], and 30 [° C.] or higher. The humidity is set to three levels, which are, from the lower humidity, lower than 40 [%], 40 [%] or higher and lower than 60 [%], and 60 [%] or higher.

As the atmospheric temperature detected by the environment sensor 614 becomes higher, or as the humidity becomes higher, the heater temperature of the air heater 613 is set to a higher temperature. If the heater temperature is set to “OFF”, power to the air heater 613 is not supplied, so that the air heater 613 is set to a temperature close to outer atmospheric temperature. For example, if the atmospheric temperature detected by the environment sensor 614 is the first temperature, that is 20 [° C.] or higher and less than 30 [° C.], and the humidity is the first humidity, that is 40 [%] or higher and less than 60 [%], the air heater 613 is set to the first heater temperature, that is, 60 [° C.]. Further, if the atmospheric temperature detected by the environment sensor 614 is the second temperature, that is, 30 [° C.] or higher, and the humidity is the second humidity, that is, 60 [%] or higher, the air heater 613 is set to the second heater temperature, that is, 90 [° C.], higher than the first heater temperature.

Similarly, the setting table of the fan output illustrated in FIG. 16 has atmospheric temperature and humidity detected by the environment sensor 614 respectively set to three levels. As for the atmospheric temperature, it is set to three levels, which are, from the lower temperature, lower than 20 [C° ], 20 [° C.] or higher and lower than 30 [° C.], and 30 [° C.] or higher. As for the humidity, it is set to three levels, which are, from the lower humidity, lower than 40 [%], 40 [%] or higher and lower than 60 [%], and 60 [%] or higher.

As the atmospheric temperature detected by the environment sensor 614 increases, or as the humidity increases, the fan output of the fans 611 a and 611 b is set to a higher output. The output of the fans 611 a and 611 b is changed, for example, by changing the rotational speed of the fans 611 a and 611 b, that is, changing the number of rotations per unit time.

For example, if the atmospheric temperature detected by the environment sensor 614 is the third temperature, that is, 20 [° C.] or higher and less than 30 [° C.], and the humidity is the third humidity, that is 40 [%] or higher and less than 60 [%], the fan output is set to the first rotational speed, that is, 40 [%]. Further, if the atmospheric temperature detected by the environment sensor 614 is the fourth temperature, that is, 30 [° C.] or higher, and the humidity is the fourth humidity, that is, 60 [%] or higher, the fan output is set to the second rotational speed, that is, 60 [%], faster than the first rotational speed.

After the heater temperature and the fan output have been determined in this manner, the control unit 700 starts blowing separation air to the sheet P supported on the lifter 507 by the air blow unit 620 (step S502). Then, after a predetermined time set in advance has elapsed from the start of blowing of separation air, the control unit 700 stops blowing separation air from the air blow unit 620 is stopped (steps S503 and S504). In this state, the shutters 615 a and 615 b operate based on a first mode. As described, by blowing separation air to the sheets P before feeding sheets, the attachment of sheets stacked on the lifter 507 can be solved, and multi feed by the pickup roller 501 can be reduced.

Next, the control unit 700 determines whether the sheet P being fed is a long sheet or not (step S505). If the sheet P being fed is not a long sheet (step S505: NO), the initial separation processing is ended. If the sheet P being fed is a long sheet (step S505: YES), as illustrated in FIG. 17, a setting screen 125 is displayed on the display operation unit 310 (step S506). The setting screen 125 includes a “shutter operation control change” button 311 for changing an operation control of the shutters 615 a and 615 b. That is, the display operation unit 310 serving as a display unit displays the setting screen 125 serving as a selection screen for selecting one of a plurality of modes including the first mode and the second mode.

Then, the control unit 700 receives change of shutter operation control from the user (step S507). In a state where the user presses the “shutter operation control change” button 311 (step S507: YES), the control unit 700 changes the shutters 615 a and 615 b from the first mode to the second mode (step S508) and ends the initial separation processing. If the user presses an “OK” button without pressing the “shutter operation control change” button 311 (step S507: NO), the control unit 700 ends the initial separation processing without changing the shutters 615 a and 615 b from the first mode.

In a state where the initial separation processing is ended, as illustrated in FIG. 12, the control unit 700 allows a job to be started (step S6). When the user presses a copy start button to enter a copy job after setting the sheets to the sheet feed deck 250 (step S7), the control unit 700 starts to blow separation air by the air blow unit 620 (step S8). Thereafter, after predetermined time set in advance is elapsed as a time required for the separation state to be stabilized, the sheet P is conveyed by the pickup roller 501 (steps S9 and S10).

If a trailing edge of a final sheet of the job is detected by the sheet feed sensor 603, the control unit 700 determines that separation of the sheet P is no longer necessary, and stops the output of separation air from the air blow unit 620 (steps S11 and S12). Thereby, the job and the sheet feed control are completed (step S13). The blowing of separation air by the air blow unit 620 is performed at least from before the feeding of the first sheet of the job is started to the feeding of the final sheet of the job is started.

In the above-described explanation of sheet feed control, the change of shutter operation control is received in a state where the “shutter operation control change” button 311 displayed on the display operation unit 310 is pressed, but the present invention is not restricted thereto. For example, the change of shutter operation control can be received automatically at a point of time when the control unit 700 acquires the sheet attribute information of the sheet P (refer to FIG. 1) being fed and determines that the sheet P being fed is a long sheet.

As described, in a state where a long sheet is fed, the operation mode of the shutters 615 a and 615 b can be changed to the second mode to narrow the opening dimension h, by which the number of sheets to which the warm air 24 a is blown can be reduced. Thereby, even if the sheet length is long, the total time during which the warm air 24 a is blown to the sheets being fed can be suppressed, and excessive reduction of moisture content of the sheet can be prevented. Thereby, paper creases transfer failures can be reduced, and the quality of the product can be improved.

Second Embodiment

Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in the contents of the initial separation processing, but it does not differ in points other than the initial separation processing. Therefore, in the present embodiment, the configurations and processing steps that do not differ from those of the first embodiment are either not shown or are denoted with the same reference numbers, and the same descriptions as the first embodiment are omitted.

In the present embodiment, in a state where the operation mode of the shutters 615 a and 615 b is changed, the influence of variation of pressure loss that occurs in the flow path is considered. For example, in a state where the operation mode of the shutters 615 a and 615 b is changed from the first mode (refer to FIG. 10A) to the second mode (refer to FIG. 10B), the opening dimensions of the exhaust ducts 617 a and 617 b are reduced. In other words, the cross-sectional areas of the flow paths FP of the exhaust ducts 617 a and 617 b are reduced. If the cross-sectional areas of the flow path FP are reduced significantly, the pressure loss of the flow paths may be increased non-ignorably. In that case, the wind speed of separation air discharged from the opening portions 612 a and 612 b may differ between the first mode and the second mode, and sheet separation ability of the separation air may be varied.

Therefore, according to the initial separation processing of the present embodiment, as illustrated in FIG. 18, a step S509 is added to the initial separation processing of the first embodiment. In step S509, the control unit 700 changes the output of the fans 611 a and 611 b according to the operation mode of the shutters 615 a and 615 b set in step S508. Specifically, in a state where the operation mode of the shutters 615 a and 615 b is changed from the first mode to the second mode, the output of the fans 611 a and 611 b is increased from the output before the change. That is, in a state where the shutters 615 a and 615 b are operated in a second mode, the rotational speed of the fans 611 a and 611 b will be faster than when the shutters 615 a and 615 b are operated in a first mode. In other words, in a state where the second mode is executed, the control unit 700 controls the fans 611 a and 611 b so that the rotational speed of the fans 611 a and 611 b is faster than when the first mode is executed. In contrast, in a state where the operation mode of the shutters 615 a and 615 b is changed from the second mode to the first mode, the output of the fans 611 a and 611 b is reduced from before the change. By changing the output of the fans 611 a and 611 b, the rotational speed of the fans 611 a and 611 b is changed.

According to the above-described operation, variation of sheet separation ability of separation air can be suppressed before and after change of operation mode of the shutters 615 a and 615 b. Therefore, the sheets can be separated preferably regardless of the selected operation mode of the shutters 615 a and 615 b.

The present invention is not restricted to the embodiments described above and can be implemented in various embodiments other than the examples described above. Various elements can be omitted, replaced or changed within the scope of the present invention. For examples, the dimensions, materials, shapes and relative arrangements of components can be altered if necessary, to apply the present invention according to the configuration and various conditions of the apparatus.

In all the embodiments described above, the sheet P stacked on the lifter 507 is fed by the pickup roller 501, but the present invention is not limited thereto. For example, the sheets stacked on the lifter 507 can be fed by attaching the sheet using negative pressure or electrostatic force. Further, the present invention is not limited to a configuration where air is blown from rotating fans 611 a and 611 b, and the present invention can also be configured to send air from an air blow portion such as a bellows pump.

In all the embodiments described above, the shutter 615 a (refer to FIG. 5B) is swung in the direction in which the warm air 24 a is passed to control the opening dimension h (refer to FIG. 5A), but the present invention is not limited thereto. For example, the exhaust ducts 617 a and 617 b may be configured to include a gate member capable of lifting and lowering between a lower end and an upper end of the exhaust ducts 617 a and 617 b to control the opening dimension at the position where the gate member is attached. Further according to the above-described embodiments, the shutters 615 a and 615 b are swung continuously during the job, but the shutters are not necessarily swung continuously during the job, and they can be stopped at a predetermined angle.

In all the embodiments described above, an example where the printer 100 (refer to FIG. 1) is equipped with the control unit 700 has been described, but the present invention is not limited thereto. The control unit 700 should merely be equipped in the image forming system 800, and for example, it can be equipped in the sheet feed deck 250.

In all the embodiments described above, an example where the opening portions 612 a and 612 b (refer to FIGS. 3 and 4) are provided on the side regulating plate 610 a serving as a regulating member has been described, but the present invention is not limited thereto. The opening portions 612 a and 612 b can be provided on the other side regulating plate 610 b (refer to FIG. 4), or they can be provided on both the side regulating plates 610 a and 610 b. Further, the opening portions 612 a and 612 b can be formed on the deck body, and the side regulating plates 610 a and 610 b can be omitted.

The printer 100 adopting an electrophotographic system was described as an example of the image forming apparatus in all the embodiments described above, but the present invention can be applied to an inkjet-type image forming apparatus that forms an image on a sheet by discharging ink from nozzles.

Other Embodiments

Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2018-181032, filed Sep. 26, 2018, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. A sheet feeding apparatus comprising: a sheet supporting portion configured to support a plurality of sheets; a sheet feeding portion configured to feed a sheet supported on the sheet supporting portion in a sheet feeding direction; an air blow unit comprising an air blower configured to blow air, an opening portion through which air blown from the air blower is blown out, a duct configured to form a flow path through which air flows between the air blower and the opening portion, an adjustment portion arranged to oppose to an upper surface of the duct and the opening portion and configured to vary an opening dimension in a height direction between the upper surface and the adjustment portion, the air blow unit being configured to separate a plurality of sheets, including an uppermost sheet, among the sheets supported on the sheet supporting portion by air blowing out from the opening portion; a drive source configured to drive the adjustment portion; and a control unit configured to execute, in a state where a length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a first length, a first mode in which the drive source is controlled such that the opening dimension is set to a first dimension, and to execute, in a state where the length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a second length that is longer than the first length, a second mode in which the drive source is controlled such that the opening dimension is set to a second dimension that is smaller than the first dimension.
 2. The sheet feeding apparatus according to claim 1, wherein the control unit is configured to control the air blower such that a rotational speed of the air blower in the second mode is faster than that in the first mode.
 3. The sheet feeding apparatus according to claim 1, wherein the adjustment portion comprises a swing member arranged in the flow path and configured to vary the opening dimension by swinging around a swing shaft positioned at a lower end portion of the swing member.
 4. The sheet feeding apparatus according to claim 3, wherein the swing member is configured to swing continuously during a sheet feeding job in which the sheet feeding portion feeds sheets, a swing angle of the swing member from a closed position becomes maximum in the first mode in a state where the opening dimension is set to the first dimension, the closed position being a position where the opening dimension becomes minimum, and a swing angle of the swing member from the closed position becomes maximum in the second mode in a state where the opening dimension is set to the second dimension.
 5. The sheet feeding apparatus according to claim 1, wherein the sheet feeding portion is a roller that is configured to be in contact with the uppermost sheet supported on the sheet supporting portion and rotate to feed the uppermost sheet, and the opening portion is arranged to be overlapped with a contact portion where the roller and the uppermost sheet come into contact when viewed in a width direction orthogonal to the sheet feeding direction.
 6. The sheet feeding apparatus according to claim 5, further comprising a regulating member configured to regulate a position of an edge portion, in the width direction, of the sheet supported on the sheet supporting portion, wherein the opening portion is formed on the regulating member.
 7. The sheet feeding apparatus according to claim 1, further comprising a heater configured to increase a temperature of air blowing out from the opening portion.
 8. The sheet feeding apparatus according to claim 7, further comprising an environment sensor configured to detect an environmental condition including a temperature and a humidity of ambient atmosphere of the sheet supported on the sheet supporting portion, wherein the control unit is configured to set the heater to a first heater temperature in a state where a temperature and a humidity detected by the environment sensor are relatively a first temperature and a first humidity, and to set the heater to a second heater temperature that is higher than the first heater temperature in a state where the temperature and the humidity detected by the environment sensor is relatively a second temperature that is higher than the first temperature and a second humidity that is higher than the first humidity.
 9. The sheet feeding apparatus according to claim 1, further comprising an environment sensor configured to detect an environmental condition including a temperature and a humidity of ambient atmosphere of the sheet supported on the sheet supporting portion, wherein the control unit is configured to control the air blower to rotate at a first rotational speed in a state where the temperature and the humidity detected by the environment sensor are respectively a third temperature and a third humidity, and to control the air blower to rotate at a second rotational speed that is faster than the first rotational speed in a state where the temperature and the humidity detected by the environment sensor are respectively a fourth temperature that is higher than the third temperature and a fourth humidity that is higher than the third humidity.
 10. The sheet feeding apparatus according to claim 1, wherein in a case where the sheet feeding portion feeds the sheet according to a sheet feeding job, the air blow unit continues to blow air through the opening portion from before a first sheet of the sheet feeding job supported on the sheet supporting portion is started to be fed until a final sheet of the sheet feeding job is started to be fed.
 11. The sheet feeding apparatus according to claim 1, further comprising a display unit configured to display a selection screen on which one of a plurality of modes including the first mode and the second mode can be selected.
 12. An image forming system comprising: a sheet supporting portion configured to support a plurality of sheets; a sheet feeding portion configured to feed a sheet supported on the sheet supporting portion to a sheet feeding direction; an air blow unit comprising an air blower configured to blow air, an opening portion through which air blown from the air blower is blown out, a duct configured to form a flow path through which air flows between the air blower and the opening portion, an adjustment portion arranged to oppose to an upper surface of the duct and the opening portion and configured to vary an opening dimension in a height direction between the upper surface and the adjustment portion, the air blow unit being configured to separate a plurality of sheets, including an uppermost sheet, among the sheets supported on the sheet supporting portion by air blowing out from the opening portion; a drive source configured to drive the adjustment portion; a control unit configured to execute, in a state where a length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a first length, a first mode in which the drive source is controlled such that the opening dimension is set to a first dimension, and to execute, in a state where the length of the sheet supported on the sheet supporting portion in the sheet feeding direction is a second length that is longer than the first length, a second mode in which the drive source is controlled such that the opening dimension is set to a second dimension that is smaller than the first dimension; and an image forming unit configured to form an image on a sheet fed from the sheet feeding portion. 